Effects of Stress on the Adaptive Immune System in Pigs

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Title: Effects of Stress on the Adaptive Immune System in Pigs
Author: Kick, Andrew Robert
Advisors: Charles Whisnant, Committee Member
Mary Tompkins, Committee Member
Glen Almond, Committee Chair
William Flowers, Committee Member
Abstract: KICK, ANDREW ROBERT. Effects of Stress on the Adaptive Immune System in Pigs. (Under the direction of Glen William Almond.) The purpose of this study was to investigate the effects of stress on the adaptive immune system in pigs. A preliminary study, using a Mycoplasma vaccination after weaning, was conducted in order to validate the use of flow cytometry. This study provided critical information required to refine the timing of blood collection and flow cytometry procedures for subsequent studies. The first study used nineteen crossbred pigs that were weaned at 18 days of age. Blood samples were collected when pigs were 11, 17, 19, 20, 21 and 25 days of age and were analyzed for peripheral blood cell percentages and concentrations of neutrophils, lymphocytes, T cell subsets, mature B cells and cortisol concentrations. Cortisol concentrations increased at weaning (p<.0001); lymphocyte concentrations tended to decrease at weaning (p=.091); and the N:L ratio (p<.0001) and CD4:CD8 ratio (p=.0459) both increased between day 20 and day 21. Age-related changes in the percentages of T cell subsets and B cells were consistent with previous reports. It was concluded that weaning is a stress-inducing event; however, weaning did not affect the composition of T cell subsets and B cells in the peripheral blood. The effects of a chronic stress induced by 5 days of mixing and crowding on the adaptive immune system were evaluated when the pigs were 47 days of age. Pigs were randomly assigned into one of two treatments: STRESS (n=9 pigs) and CONTROL (n=10 pigs). Peripheral blood was examined on days 47, 52, 53, 54, 55 and 62 for the same measures described previously and additionally for in-vitro IFN-γ and IL-4 production following ConA stimulation. Though there were some significant differences between the treatments upon conclusion of the stress, the STRESS pigs did not appear to be immunologically compromised. The second study used twenty-three crossbred pigs and examined the effects of weaning age on the adaptive immune system. Pigs were randomly assigned to one of three treatments: weaning at 14 (n=8 pigs), 21 (n=7 pigs) or 28 (n=8 pigs) days of age. Peripheral blood was obtained when pigs were 13, 15, 20, 22, 27, 29 and 35 days of age and analyzed for the same stress-related variables evaluated in the first study. In all treatments, weaning affected cortisol concentrations (p<.0001) and body weight percent change (p<.017). Lymphocyte concentrations displayed a treatment effect for pigs weaned at 14 days of age (p=.0744) and at 28 days of age (p=.0139). Other significant differences occurred between treatments; however, the differences were not directly associated with weaning. Based upon the immunological measures utilized in this study, there was not an explicit benefit to the adaptive immune system for any weaning age. In summary, chronic stress and early weaning do not negatively affect the adaptive immunological competence of pigs as determined by changes in populations of immune cells and cortisol concentrations. Additional studies comparing chronic stress or weaning age in a commercial herd and its effect on disease frequency are required in order to adjudicate for issues of animal welfare.
Date: 2010-06-30
Degree: MS
Discipline: Physiology
URI: http://www.lib.ncsu.edu/resolver/1840.16/6349


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